Large storage systems (e.g., enterprise level storage) typically include multiple individual storage devices (e.g., disk drives). The individual storage devices are accessed by host systems via Input/Output (I/O) requests, such as reading and writing, through one or more storage controllers. Examples of large storage systems include, without limitation, Redundant Array Of Independent Disks (RAID) storage systems that have one or more logical units (LUNs) distributed over a plurality of disks, and spanned volumes (e.g., non-RAID architecture; JBOD, etc.). Examples of the host systems include computing environments, ranging from individual personal computers and workstations to large networked enterprises encompassing numerous types of computing systems. A variety of well-known operating systems may be employed in such computing environments depending upon the needs of particular users and enterprises. Storage devices in such large storage systems may include standard hard disk drives as well as other types of storage devices such as solid-state drives (SSD), optical storage, semiconductor storage (e.g., Random Access Memory disks or RAM disks), tape storage, et cetera.
In any large storage system, a limiting feature in processing I/O requests is latency in accessing individual storage devices It will be appreciated that access speeds of many electronic storage components, such as SRAM, DRAM and solid state memory devices, continue to increase, often exponentially. The same has not tended to for mechanical storage components, such as those found in rotating storage media. For instance, seek latency of a rotating hard drive is limited by actuator arm speed and disk circumference, and throughput of such a rotating hard drive is limited by the rotational speed of the disk. Thus, access speeds of rotating storage media are considerably slower than access speeds of electronic storage components Nonetheless, as rotating storage media continues to be among the most economical storage solution for mass storage systems, it remains in extensive use.
To improve performance of storage systems utilizing rotating storage media, a number of large storage systems have begun to implement higher level caches of increasing size to allow preloading increased amounts of data into cache. In this regard, high demand data from the rotating storage media may be preloaded into the higher level cache(s). Upon receiving a read request for data, pre-loaded data may be retrieved free of accessing rotating media.